IGMA Offers New Glazing Guidelines for IG

Publication can help residential and commercial fenestration fabricators avoid potentially costly problems

Improper glazing is one of the leading causes of premature failure of insulating glass units. Whether it is due to prolonged water exposure, improper glazing clearances, improper use of setting blocks and spacer shims or component incompatibility, problems associated with glazing IG units into a window or door can be costly for manufacturers of all types of products.

A new publication from the Insulating Glass Manufacturers Alliance provides advisory glazing guidelines to assist in achieving long-term performance for sealed insulating glass units. Topics covered in the new publication include glass types, framing, glazing clearances, setting blocks, spacer shims and glazing materials. Additionally, the document includes chapters on receiving, storage and handling and glass protection and cleaning. Intended for use by those who design, specify, manufacture and install IG units, the document is the result of open discussions and review by IGMA’s glazing guidelines working group.

Since its formation in October 2000—a result of the merger between the Sealed Insulating Glass Manufacturers Association and the Insulating Glass Manufacturers Association of Canada—IGMA has been reviewing all of the predecessor organizations’ publications as required under its ISO 9000 quality management system. Since SIGMA and IGMAC had separate glazing guidelines, IGMA decided to harmonize the two documents into one publication.

The SIGMA guidelines were written to provide members with detailed guidelines specific to commercial and residential applications, with more emphasis on the commercial side. IGMAC’s publication also covered both residential and commercial applications, but much more generically. It also offered detailed glazing diagrams. The IGMA publication combines the best of each, in addition to technical updates, prescriptive and performance-based recommendations, charts and detailed diagrams. The document was completed at IGMA’s August 2004 summer meeting and published last October as TM-3000-90 (04).

While the original SIGMA and IGMAC documents did not differentiate between residential and commercial units, the new guidelines make clear what is applicable for residential and commercial glazing. In some circumstances, the criteria overlap, and readers should recognize the differences. For example, Figure 1, along with Tables 1 and 2—taken from the new guide’s section on glass coverage or bite—reflect how the new document provides users with information on both commercial and residential applications. References to commercial applications include the American Architectural Manufacturers Association’s Aluminum Curtain Wall Design Guide Manual.

The section on setting blocks is another example where IGMA made significant modifications to better cover both residential and commercial applications. To ensure compatibility and consistency between fenestration industry standards and specifications, this section was developed in consultation with members of AAMA and the Window & Door Manufacturers Association, who were developing the harmonized AAMA/WDMA/CSA 101/I.S.2/A440 standard for windows, doors and unit skylights.

Proper Drainage
One topic the document emphasizes is that proper drainage of the glazing channel is a key element in maximizing the life of an IG unit. Virtually all IG fabricators warn of the consequences of improper glazing system drainage. In addition, IG warranties often state that they do not apply to products that have been subjected to prolonged exposure to water or saturated water vapor. Prolonged exposure to water or moisture vapor in a glazing channel is the number one cause of seal failure in IG units. The IGMA publication explains how glazing systems must be designed with a means of completely draining infiltrated water at a rate equal to or greater than the rate of infiltration.

The publication also outlines how the face of an IG unit should be cushioned from the adjacent framing system with glazing gaskets, sealants, spacers or tapes. All such materials must be continuous and thick enough to maintain proper clearance between the framing system, the face of the glass and the edges of the glass in order to prevent breakage. Narrow face clearances can cause a clamping effect on the glass edges, the publication notes. The resulting glass stresses with clamped edges can readily cause annealed glass breakage. The desired “simple” support supplied by normal face clearances greatly reduces the bending stress in glass with ambient air temperature and pressure changes.

The chapter on setting blocks explains how these components give the IG unit a cushion support and ensure a space is created to allow the sash and frame some room for deflection without applying stress to the unit itself. It also explains the role of setting blocks in allowing an area for possible water accumulation in the sash or frame. The water can than easily flow to and out the weep or vent holes. Finally, the guidelines cover how setting blocks provide proper positioning of the IG unit in the daylight opening.

Provided as a service to the industry, the guidelines reflect the collective experiences of IG manufacturers, glass and glazing material suppliers, design engineers, industry consultants and persons and firms experienced in successful glazing techniques. Although not a specification, these guidelines can be helpful to window and door manufacturers in their product design and development efforts, as well as their IG fabrication and glazing operations. The IGMA guidelines are not intended to exclude other possible glazing practices and reflect those practices that over the years have led to successful field performance of sealed insulating glass units. Users are always encouraged to seek professional advice for specific glazing applications, which differ from those detailed in these guidelines. Copies of the new guidelines and other IGMA publications can be ordered at www.igmaonline.org/publications or by contacting the association’s office at 613/233-1510.